Disk drive suspension with multi-layered piezoelectric actuator controlled gram load

ABSTRACT

A method and apparatus for actively controlling the gram load on a disk drive suspension assembly and to a disk drive using the present disk drive suspension assembly. The gram load can be actively changed by changing the applied voltage to one or more multi-layer piezoelectric actuators attached to the head suspension. The active gram control system allows the gram load to be changed on a non-permanent basis and to control the gram load to a much finer scale than can be accomplished using conventional techniques. The disk drive suspension that uses a piezoelectric actuator having two or more layers. Each layer of the multi-layer piezoelectric actuator is poled in such a fashion that when energized, some piezoelectric layers contract while others expand, resulting in a curling motion. By attaching the first and second ends of the piezoelectric actuator to discrete locations on the load beam, while the portion of the piezoelectric actuator between the first and second ends remains unattached to the load beam, a force non-parallel to the load beam can be applied to the head suspension.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for activelycontrolling the gram load on a disk drive suspension assembly and a diskdrive using the present disk drive suspension assembly.

BACKGROUND OF THE INVENTION

Head suspension assemblies are commonly used in rigid magnetic diskdrives to support magnetic heads in close proximity to the rotating disksurfaces. Head suspension assemblies of this type typically include anair bearing head slider assembly mounted to a suspension. The suspensionincludes a load beam having a mounting region on its proximal end and agimbal or flexure on its distal end. When incorporated into a diskdrive, the mounting region is mounted to an actuator or positioning arm,which supports the suspension assembly over the rotating disk. Abaseplate is typically welded to the mounting region to increase therigidity of the mounting region and to provide a mechanism for securelymounting the suspension assembly to the positioning arm.

The load beam is an elongated and often generally triangularly shapedmember that includes a spring region adjacent to the mounting region,and a rigid region that extends from the spring region. The flexure canbe manufactured as a separate member and welded to the distal end of theload beam, or formed as an integral member in the distal end of the loadbeam.

The air bearing head slider assembly contains a magnetic head and istypically bonded to the flexure by adhesive. The flexure allows the headslider assembly to move or “gimbal”(about rotational pitch and rollaxes) with respect to the distal end of the load beam and thereby followvariations in the surface of the spinning disk. To enable the pivotalflexure movement, the surface of the flexure to which the head sliderassembly is bonded is typically spaced from the adjacent surface of theload beam by structures known as load point dimples or formed offsets.

Suspensions are commonly manufactured by chemically etching flat orunformed load beam blanks from thin sheets of stainless steel. Flat andunformed flexure blanks are etched in a similar manner from sheets ofstainless steel. During subsequent manufacturing operations, side rails,load point dimples and any other structures that extend upwardly ordownwardly from the web or generally planar surface of the load beam areformed on the load beam blanks by mechanical bending procedures. Anydimples, offsets or other structures on the flexures requiringdeformation of this type are formed in a similar manner. After forming,the flexures are welded to the distal end of the load beams. Baseplatesare also welded to the suspensions following the forming operations.

The product of these etching, welding and forming operations aregenerally flat suspensions (i.e., the mounting region, spring region andrigid region of the load beam are generally coplanar and at the sameheight. During subsequent manufacturing operations, at least a portionof the spring region of the load beam is rolled around a curved mandrelor otherwise bent in such a manner as to plastically bend or permanentlydeform the spring region. The rolling operation imparts a curved shapeto the spring region and causes the flexure to be offset from themounting region when the suspension is in its unloaded or free state.

As noted above, the suspension supports the slider assembly over themagnetic disk. In one embodiment, air pressure at the surface of thespinning disk creates a positive pressure air bearing that causes theslider assembly to lift away from and “fly”over the disk surface. Inanother embodiment, a negative pressure air bearing pulls the sliderassembly toward the disk surface. To counteract these hydrodynamicforces, the head suspension assembly is mounted to the disk drive withthe suspension in a loaded state so the bent spring region of thesuspension biases the head slider assembly either toward or away fromthe magnetic disk. The height at which the slider assembly flies overthe disk surface is known as the “fly height.”The force exerted by thesuspension on the slider assembly when the slider assembly is at flyheight is known as the “gram load.”

By controlling the gram load of the head suspension, the force appliedto the read/write head at a constant flying level can be determined.Current suspensions have a gram load that is determined by a bend radiusin the suspension arm. The accuracy of this type of gram loading methodis typically about +/−0.1 grams. Once bent into position, the suspensionarm has no way of changing the gram load, unless subsequently bent oraltered in a permanent way.

U.S. Pat. No. 5,898,541 (Boutaghou et al.) discloses a bi-morphpiezoelectric bending motor mounted on the head slider. The bendingmotor cooperates with a tab surface on the flexure to rotate the slider.

U.S. Pat. No. 5,719,720 (Lee) discloses a load beam of a head suspensionmechanism that has a non-load bearing, single layer of piezoelectricmaterial on at least one surface of a resilient portion of the loadbeam. A controller apparatus provides a control signal to thepiezoelectric material that induces expansion or contraction of thepiezoelectric material to cause the load beam to raise the head sliderfrom the surface in the disk drive. Since the piezoelectric material ofthe '720 patent is limited to compression and expansion forces, it mustbe attached directly to the surface of the load beam. Consequently, thecompression or expansion of the single layer piezoelectric materialoccurs along the length of the load beam and must overcome the stiffnessof the load beam to produce a bending or curving motion of the resilientportion of the load beam. That is, the forces generated by thecompression or expansion of the piezoelectric material are parallel tothe surface of the load beam. Directing the forces from thepiezoelectric material parallel to the load beam limits the amount ofdeflection and load applied to the load beam.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus for activelycontrolling the gram load on a disk drive suspension assembly and to adisk drive using the present head suspension. The gram load can beactively changed by changing the applied voltage to a multi-layerpiezoelectric material attached to the head suspension. The active gramcontrol system of the present invention allows the gram load to bechanged on a non-permanent basis and to control the gram load to a muchfiner scale than can be accomplished using conventional techniques. Thepresent active gram control system may also be used for active vibrationdamping, lifting the read/write head, a shock sensor, and for contactrecording.

The present invention is directed to a disk drive suspension assemblythat uses at least one piezoelectric actuator having two or more layers.In a two-layer embodiment, each layer of the multi-layer piezoelectricactuator is poled in such a fashion that when energized, onepiezoelectric layer contracts while the other expands, resulting in acurling motion. In an embodiment with more than two layers, thepiezoelectric actuator is poled to achieve a curling motion. Byattaching the first and second ends of the piezoelectric actuator todiscrete locations on the load beam, while the portion of thepiezoelectric actuator between the first and second ends remainsunattached to the load beam, a force that is non-parallel to the surfaceof the load beam can be applied to the head suspension. In oneembodiment, the force is normal to the load beam.

In one embodiment, the load beam may include a compliant region locatedbetween the first and second attachment locations for the piezoelectricactuator. Consequently, the piezoelectric actuator in an unactuatedstate supports a portion of the gram load. By arranging the multi-layerpiezoelectric to span across the compliant region, a greater range ofmotion and a greater range of gram loading can be achieved. Compliantregion refers to a partial etch, a hole, a recess, a narrowing of theload beam, one or more lines of weakness extending generally laterallyacross load beam, or other features in the load beam that create alocation of flexibility greater than elsewhere along the load beam.

The present invention is also directed to a disk drive using the presentdisk drive suspension assembly. The disk drive includes a rigid magneticdisk and a positioning arm attached to the actuator arm mounting region.The head mounting region on a distal end of the load beam includes atleast one transducer head positioned opposite the rigid magnetic disk.The piezoelectric actuator has at least two layers. First and secondends of the piezoelectric actuator are attached to the load beam atfirst and second attachment locations, respectively, so that a forcenon-parallel to the load beam is applied to the head suspension in anactuated state. In one embodiment, the force is normal to the load beam.

The multi-layer piezoelectric actuator can be used to determineprecisely the flying height of the read/write heads on the disk drivesuspension. Moreover, the gram load can be changed with changing driveconditions. The multi-layer piezoelectric actuator can eliminate theneed for an active head lifter and landing zones on the fixed disk,while protecting the read/write heads during periods of inactivity.Since the layers of the multi-layer act as both actuators andtransducers, the various layers produce a voltage when deflected. In oneembodiment, these voltages are extracted to dampen gram changingvibrations and deflections. In another embodiment, the extractedvoltages can be actively counteracted to reduce gram changingvibrations.

The present invention is also directed to a method of making a diskdrive suspension assembly in accordance with the present invention. Aload beam is formed having a distal end, an actuator arm mounting regionon a proximal end, a rigid region, and a spring region between the rigidregion and actuator arm mounting region. A compliant region is formed inthe load beam. A head mounting region is formed on a distal end of theload beam for receiving a transducer head. A piezoelectric actuatorhaving at least two layers is assembled. First and second ends of thepiezoelectric actuator are attached to first and second attachmentlocations on opposite sides of the compliant region of the load beam sothat the piezoelectric actuator supports a portion of the gram load inan unactivated state. The method may include the step of applying avoltage to one at least one of the piezoelectric actuators to performone or more of controlling the flying height of the head mountingregion, modifying the gram load, raising or lowering the head mountingregion, measuring vibrations and deflections of the load beam, dampeningvibrations of the load beam, controlling attitude of the head mountingregion, and applying a lateral force on the load beam.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic illustration of a disk drive suspension assemblyin accordance with the present invention.

FIG. 1A is a sectional view of an alternate piezoelectric actuator inaccordance with the present invention.

FIG. 2 is a top schematic illustration of the disk drive suspension ofFIG. 1.

FIG. 2A is a top schematic illustration of an alternate disk drivesuspension in accordance with the present invention.

FIG. 3 is a top schematic illustration of an active attitude controlsuspension assembly in accordance with the present invention.

FIG. 4 is a top schematic illustration of disk drive in accordance withthe present invention.

FIG. 5 is a graph of gram load versus voltage for one embodiment of thedisk drive suspension assembly of the present invention.

FIG. 6 is a graph of gram load versus voltage for another embodiment ofthe disk drive suspension assembly of the present invention.

FIG. 7 is a graph of gram load versus voltage for various designs ofdisk drive suspension assemblies.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 are side and top views of a disk drive suspension assembly20 in accordance with the present invention. Head suspension 22 includesa load beam 24 having a mounting region 26 on its proximal end and agimbal or flexure 28 on its distal end. A base plate 30 is typicallywelded to the mounting region 26 to increase the rigidity of themounting region 26 and to provide a mechanism for securely mounting thedisk drive suspension assembly 20 to an actuator or positioning arm 157on a disk drive 150 (see FIG. 4). The load beam 24 is an elongated andoften triangular shaped member that includes a spring region 32. Rigidregion 34 is the portion of the load beam that extends between thespring region 32 and the distal end 36.

The mounting region 26 is typically rigid. In the illustratedembodiment, the mounting region 26 includes a compliant region 58. Forgram control applications, the compliant region 58 is compliant in the zdirection 56. For lateral control applications (see FIG. 3), thecompliant region 58 is compliant in the x and y directions.

A multi-layer piezoelectric actuator 40 is mounted to the load beam 24at first and second attachment locations 42, 44 using an adhesive. Inone embodiment, the adhesive is conductive, such as an adhesive soldunder the product designation XP 501, available from EMI Corporation ofBreckenridge, Colo. The first and second attachment locations 42, 44 arepositioned on opposite sides of the compliant region 58. In theillustrated embodiment, the first attachment location 42 is adjacent tothe base plate 30, but does not touch the base plate 30 and the secondattachment location 44 is adjacent to the spring region 32, but does notextend onto the spring region. The piezoelectric actuator 40 is notbonded to the load beam 24 between the attachment locations 42, 44.

In the illustrated embodiment, the multi-layer piezoelectric actuator 40is a two-layer piezoelectric actuator with a middle electrode 46. Themulti-layer piezoelectric actuator 40 illustrated in FIG. 1 is of a stepconstruction. This construction allows electrical connection 47 to themiddle electrode 46 to be bonded directly to lower piezoelectric element54. A middle electrode that protrudes from one side of the multi-layerpiezoelectric actuator 40 may also be used. Alternatively, one of thepiezoelectric layers 52, 54 may include a hole for accessing the middleelectrode 46.

An electric field can be applied to a piezoelectric actuator 40 to causeit to deform. Alternatively, when pressure is applied to thepiezoelectric actuator 40, the actuator 40 generates an electric fieldin proportion to the pressure applied. That is, the piezoelectricactuator 40 has a reversible relationship between physical deformationand electric energy. The piezoelectric layers 52, 54 may be constructedfrom a variety of materials, such as lead zirconium titinate, polymerssuch as polyvinylidene fluoride (PVDF), or other piezoelectric orelectrostrictive types of materials.

In the embodiment of FIG. 1, voltage is applied to the middle electrodelayer 46, while the top and bottom surfaces 48, 50 are grounded, tocreate an actuated state. Each of two piezoelectric elements 52, 54 arepoled in the same direction. When energized, one piezoelectric layercontracts, while the other expands. The curling motion occurs when thetwo piezoelectric elements 52, 54 exert opposite forces on each other.The resulting force is non-parallel to the surface of the load beam 24.In one embodiment, the force is normal to the load beam along the z-axis56. The force can be either positive or negative. The gram load can beactively changed by changing the voltage applied. Alternatively, themiddle electrode layer 46 is grounded and voltage is applied to the topand bottom surfaces 48, 50.

Due to the location of the compliant region 58, the piezoelectricactuator 40 in the unactuated state carries some fraction of the totalgram load. That is, the piezoelectric actuator 40 contributes to thegram load of the suspension assembly 20 in an unactuated state. Theunactuated state refers to zero voltage being applied across thepiezoelectric actuator 40. Only the distal ends of the piezoelectricactuator 40 are adhered to the load beam 24 at locations 42, 44, so asto not inhibit the curling motion. The complaint region 58 is typicallythe weakest point on the load beam 24 between the attachment locations42, 44. Consequently, when a voltage is applied to the piezoelectricactuator 40, the load beam 24 is bent or flexed primarily at thecompliant region 58.

The size and shape of the piezoelectric actuator 40 can be changed toincrease or decrease the range of gram load available for application tothe disk drive suspension assembly 20. Also, the location, shape and/ordepth of the compliant region 58 that is spanned by the piezoelectricactuator 40 can be changed to modify the percentage of the gram loadcarried by the piezoelectric actuator 40. The location of thepiezoelectric actuator 40 and corresponding compliant region 58 can belocated anywhere along the suspension assembly 20. In the illustratedembodiment, the stiffness of the base plate 30 provides the structureagainst which the piezoelectric actuator 40 acts in the actuated state.

Piezoelectric actuators with more than two layers may also be used inthe present invention, such as the bi-morph piezoelectric actuator shownin U.S. Pat. No. 5,898,541 (Boutaghou et al.). FIG. 1A is a crosssectional illustration of a piezoelectric actuator 200 with four layers202, 204, 206 and 208. Electrode surfaces 210, 214, 220 and 222 form afirst electrode A. Electrode surfaces 212, 216 and 218 form a secondelectrode B. The arrows indicate the direction of polarization.Electrode surface 220, 218 connected to electrodes A and B,respectively, partially extend across the top surface of thepiezoelectric actuator 200. Electrode surface 222, 216 connected toelectrodes A and B, respectively, partially extend across the bottomsurface of the piezoelectric actuator 200. The ends of the layers 202,204, 206 and 208 are covered by the electrodes A and B, but the sidesare not. When electrodes A and B have a voltage differential, the toptwo layers 202, 204 will contract, while the bottom two layers 206, 208will expand, or visa-versa, creating a curling motion.

FIG. 2A is a top view of an alternate disk drive suspension 70 inaccordance with the present invention. The suspension 70 includes a loadbeam 72 having a mounting region 74 on its proximal end and a gimbal orflexure 76 on its distal end. A base plate 78 is welded to the mountingregion 74. The load beam 72 is an elongated member that includes aspring region 80 and a rigid region 82 extending between the springregion 80 and the flexure 76. In the illustrated embodiment, a compliantregion 84 is formed in the rigid region 82 between the spring region 80and the flexure 76. A multi-layer piezoelectric actuator 86 is attachedto the load beam 72 at first and second attachment locations 88, 90using an adhesive. The first and second attachment locations 88, 90 arepositioned on opposite sides of the compliant region 84. Thepiezoelectric actuator 86 is not bonded to the load beam 72 between theattachment locations 88, 90.

FIG. 3 is a schematic illustration of a disk drive suspension 100 havinga pair of multi-layer piezoelectric elements 102, 104 that provideactive attitude control. The piezoelectric actuators 102, 104 aremounted along the edges of the spring region 106 and extend over or spana compliant region 108. In the illustrated embodiment, the attachmentlocations of the piezoelectric actuator 102 are coplanar with theattachment locations of the piezoelectric actuator 104. By selectivelyactuating one or both of the piezoelectric actuators 102, 104, and/oractivating them in opposite directions, a torque can be applied to theload beam 110. The active attitude control provided by the piezoelectricactuators 102, 104 permits different rotational forces on the read/writehead on flexure 112, thus allowing for partial control of staticattitude.

For example, the disk drive suspension 100 may be used for lateralactuation by applying a voltage to the piezoelectric actuators 102, 104.By having one of the actuators 102 expand and the other actuator 104contract, or visa versa, lateral motion of the read/write head 112 canbe generated along the x-axis 114 and the y-axis 116. The actuators 102,104 may also be used for controlling the gram forces on the suspension100.

FIG. 4 is a schematic illustration of a rigid magnetic disk drive 150 inaccordance with the present invention. Head suspension assembly 152includes a load beam 154 with magnetic heads and a flexure 156 at adistal end and a mounting region 155 attached to an actuator arm 157.The proximal end of the head suspension assembly 152 is mounted to arotary actuator 158. The head suspension assembly 152 positions themagnetic heads and flexure 156 in close proximity to a rotating disk160. A multi-layer piezoelectric actuator 162 is attached to the loadbeam 154 at attachment locations 164, 166 positioned between the springregion 170 and the mounting region 155. In one embodiment, a compliantregion 168 is formed in the load beam 154 between the attachmentlocations 164, 166 to form a load bearing piezoelectric actuator.

The multi-layer piezoelectric actuator 162 can be used to determineand/or precisely control the flying height of the read/write heads 156over the rotating disk 160 on a real-time basis. In another embodiment,the gram load of the head suspension assembly 152 can be changedreal-time with changing drive conditions. The multi-layer piezoelectricactuator 162 can eliminate the need for an active head lifter andlanding zones on the rotating disk 160, while protecting the read/writeheads 156 during periods of inactivity. Since the layers of themulti-layer piezoelectric actuator 162 act as both actuators andtransducers, the various layers produce a voltage when deflected.Extracting these voltages reduces the energy in the assembly 152 anddampens vibrations and deflections. In another embodiment, the extractedvoltages are used to quantify the vibrations and a corresponding voltageis applied to the actuator 162 to actively dampen vibrations. Variouselectronic control circuits for controlling the piezoelectric actuator162 to perform the functions discussed herein are disclosed in U.S. Pat.No. 5,377,058 (Good et al.); 5,719,720 (Lee); and U.S. Pat. No.5,802,701 (Fontana et al.).

Construction of an Active Gram Control Suspension Load Bearing,Multi-Layer Piezoelectric Actuator

A head suspension was constructed with a load bearing, multi-layerpiezoelectric actuator in accordance with the present invention. Thehead suspension was constructed from a Magnum 5 head suspensionavailable from Hutchinson Technology Inc. located in Hutchinson, Minn.The piezoelectric material used for the piezoelectric actuator wasobtained from Motorola Corporation in Albuquerque, N.Mex. under theproduct designation 3203HD.

Pieces of the piezoelectric about 0.125 millimeters (mm) thick were cutinto pieces about 2.25 mm wide and about 10.5 mm long using the dicingsaw. The Motorola 3203HD material had Au electrode material on bothsides. The pieces were then shortened using a diamond scribe to lengthsof approximately 5 mm to about 7 mm. Pieces of the piezoelectric withdifferent lengths were bonded together using EMI XP 501 conductiveepoxy, available from EMI Corporation of Breckenridge, Colo. The epoxywas cured in an ultra-clean oven at about 145 degrees ° C. for about 5minutes. The poling direction of each piezoelectric layer was kept inthe same direction for their construction.

The Magnum 5 head suspension has an etched region in the load beam thatforms a compliant region. The distal ends of the load bearing,multi-layer piezoelectric actuator were attached to the head suspensionusing EMI XP 501 conductive epoxy. The attachment locations were nearthe base plate and on the opposite side of an etched region. By spanningthe etched region, the multi-layer piezoelectric actuator provided aportion of the gram load for the head suspension. The piezoelectricactuator was arranged so that the longer piece of piezoelectric materialwas bonded to the load beam, with the stepped surface located away fromthe base plate (see for example FIG. 1). The bonds were approximately0.4 mm in length and extended the width of the piezoelectric actuator(2.25 mm). The region between the attachment locations was not bonded tothe head suspension. The epoxy was cured for 5 minutes at 145° C. in theultra-clean oven.

Non-Load Bearing Multi-Layer Piezoelectric Actuator

Using the procedure and materials discussed above, a head suspensionwith a non-load bearing multi-layer piezoelectric actuator wasconstructed. For this design, the piezoelectric material was cut intopieces approximately 3 mm and 5 mm in length. The multi-layerpiezoelectric actuator was attached to a Magnum 5 head suspension usingthe conductive epoxy. The attachment locations were near the base plateand adjacent to the side of the etched region closest to the base plate.The piezoelectric actuator did not span the partial etched region of theMagnum 5 suspension and did not provided any support to the etchedregion. The bonds were approximately 0.4 mm in length and extended thewidth of the piezoelectric actuator (2.25 mm).

Load Bearing Single Layer Piezoelectric Actuator

Using the procedure and materials discussed above, a head suspensionwith a load bearing, single layer piezoelectric actuator wasconstructed. Only one piece of piezoelectric material, approximately 7mm long, was bonded to the Magnum 5 suspension. Conductive epoxy was useto bond the piezoelectric actuator to areas on both sides of the partialetch region. Larger areas of conductive adhesive, approximately 2 mm inlength and 2.25 mm in width were applied to the load beam.

Testing of the Head Suspensions

The head suspensions were tested for gram control and gram range usingan EK120 load cell, available from Berne Scale, Minneapolis, Minn. Theload cell was sensitive to 0.01 grams. Load was applied to the headsuspensions using an ORIEL Model 18011 Encoder Mike Controller and anORIEL Encoder Mike stepping motor. The gram load fixture was somewhataffected by external noise, vibrations and air flow. The measured gramload reading was observed to drift by 0.02-0.03 grams with time and/orexternal perturbation.

For the test, the head suspensions were loaded with approximately twograms. Voltage to the piezoelectric actuator was supplied by a Keithley2400 source meter. Electrical connections to the piezoelectric actuatorwere made using soldered on wires.

Example 1

Example 1 examined the gram load to applied voltage for the headsuspension with the load bearing, multi-layer piezoelectric actuator.

The wires were soldered to the top surface and the stepped surface ofthe piezoelectric actuator. The base of the suspension and the topsurface of the piezoelectric actuator were grounded, and voltage wassupplied to the stepped middle electrode.

Voltage to the piezoelectric actuator was applied in 5 volt increments.In the first test, the voltage was applied from zero to +30 volts andthen stepped to −30 volts and back to 0 volts. At each 5 volt increment,the gram was recorded. FIG. 5 shows a graph of the measured gram loadversus applied voltage with a gram load ranging between about 1.67 gramsand about 2.33 grams. The sensitivity of the gram-to-voltage calculatedfrom the slope of the curve is 0.011 grams/volt.

Example 2

Example 2 examined the gram load to applied voltage for the headsuspension with the load bearing, multi-layer piezoelectric actuator.

Voltage to the piezoelectric actuator was applied in 5 volt increments.In the second test the voltage was applied from zero to +50 volts andthen stepped to −50 volts. At each 5 volt increment, the gram load wasrecorded. FIG. 6 shows a graph of the measured gram versus appliedvoltage with a gram load ranging between about 1.42 grams and about 2.66grams. The sensitivity of the gram-to-voltage calculated from the slopeof the curve is 0.0124 grams/volt. The sensitivity of gramload-to-voltage is dependent on the piezoelectric actuator andsuspension design. A head suspension could be designed for a particularsensitivity.

FIGS. 5 and 6 show some hysteresis in the curves of gram load versusapplied voltage. Hysteresis is inherent in some piezoelectric materials.Use of a charge control system, instead of voltage control system, hasthe potential to reduce the hysteresis.

FIGS. 5 and 6 show the ability of the head suspension to control gramload with applied voltage. Depending on the magnitude of the voltage, arange of up to 1.24 grams (+/−50 volts) can be attained with the headsuspension. A larger range of gram control could be achieved in severalways, such as increasing the applied voltage, using a wider actuatordesign, increasing the gram load carried by the actuator, and changingthe location, shape and size of the actuator and/or the compliantregion. Current Underwriter Laboratories specification 1950 for SELVClass II circuitry within hard disk drives limits the usable voltage to+/−30 volts.

Example 3

Example 3 examined the gram load and sensitivity of the head suspensionwith the load bearing, multi-layer piezoelectric actuator.

To determine the accuracy to which the gram load of the head suspensioncould be controlled, gram load levels of 1.75 grams and 2.25 grams werechosen as target values. To start the test, the nominal gram level wasmeasured at 0 applied volts. Voltage was then slowly applied until thetarget gram load was met. The voltage at the target gram load was thenrecorded. Results of the test are shown in Table 1.

TABLE 1 Gram Load at 0 Attained Gram Target Gram Load Volts Load AppliedVoltage 1.75 grams 2.03 grams 1.75 grams −26 volts 2.25 grams 2.05 grams2.25 grams  21 volts

Example 3 shows that the present head suspension can control the gramload to within 0.01 grams accuracy, or a factor of 10 more accuratelythan conventional gram loading techniques. Gram levels of 2.25 and 1.75grams were achieved by simply increasing or decreasing the voltage untilthe gram load met the target values. The piezoelectric actuator shouldbe able to control gram load as accurately as the input voltage iscontrolled. If the input voltage is accurate to within 1.0 volts, gramload on the head suspension should be controlled at increments of 0.01grams. Potentially, the voltage could be controlled at a much finerresolution than 1.0 volts, and thus the gram control would be finer than0.01 grams.

Example 4

Example 4 examined the gram load range and gram control for the threedifferent head suspension having a load bearing, single layer actuator,a load bearing, multi-layer actuator and a non-load bearing, multi-layeractuator.

The base of the head suspension and the top surface of the multi-layerpiezoelectric actuators were grounded, and voltage was supplied to thestepped multi-layer piezoelectric actuator surface. For the single layerpiezoelectric actuator, the load beam was ground, and voltage wassupplied to the top surface of the piezoelectric actuator.

For each test, the suspension was loaded with approximately 2 grams ofload. The voltage was stepped up in 5 volts increments to +25 volts, andthe gram was recorded at each increment. The voltage was then steppeddown to 0 volts in 5 volt increments, and the gram was recorded at eachincrement. FIG. 7 is a graph showing the measured gram with appliedvoltage for each of the tests.

Curve 180 of FIG. 7 shows the performance of the load-bearing,multi-layer piezoelectric actuator. As compared with the load-bearing,multi-layer piezoelectric actuator, the performance of the non-loadbearing, multi-layer piezoelectric actuator shown in curve 182 was aboutone seventh the gram load range. The performance of the load bearing,single layer piezoelectric actuator shown in curve 184 was about onefourth the gram load range of the load bearing, multi-layerpiezoelectric actuator.

Gram measurement tests were performed to determine the performancedifferences between gram control suspension that used either a loadbearing multi-layer piezoelectric actuator, a non-load bearingmulti-layer piezoelectric actuator or a load bearing, single layerpiezoelectric actuator. A summary of the sensitivity data is provided inTable 2.

TABLE 2 measured gram suspension type voltage range range sensitivityload-bearing, multi- 0 to +25 volts 1.99 to 2.21 grams 8.8 mg/v layerpiezoelectric actuator non-load bearing, 0 to +25 volts 2.05 to 2.08grams 1.2 mg/v multi-layer piezoelectric actuator load bearing, single 0to +25 volts 2.05 to 2.10 grams 2.0 mg/v layer piezoelectric actuator

The data in Table 2 shows a significant improvement in gram control forthe load-bearing, multi-layer piezoelectric actuator. The sensitivity ofthe load bearing, multi-layer piezoelectric actuator was four timesgreater than the load bearing, single layer piezoelectric actuator. Thisdata also shows that allowing the actuator to bear part of the gram loadwas a significant factor in the performance of the active gram controlsuspension.

The load bearing, multi-layer piezoelectric actuator showed asignificant improvement in control of gram forces over the load bearing,single layer piezoelectric actuator design. This improvement appears tobe the result of the increased force that the multi-layer piezoelectricactuator can produce and the direction of that force. The load bearing,single layer piezoelectric actuator design limits the amount of changein gram load controlling forces. It is expected that non-load bearing,single layer piezoelectric actuators would perform even worse than theload bearing, single layer piezoelectric actuator due to the increasestiffness of the load beam.

The complete disclosures of all patents, patent applications, andpublications are incorporated herein by reference as if individuallyincorporated. Various modifications and alterations of this inventionwill become apparent to those skilled in the art without departing fromthe scope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A disk drive suspension assembly, comprising: aload beam having a distal end, an actuator arm mounting region on aproximal end, a rigid region, and a spring region between the rigidregion and actuator arm mounting region; a head mounting region on adistal end of the load beam for receiving a transducer head; and atleast one multi-layered piezoelectric actuator having at least twolayers attached to each other along a common surface, the piezoelectricactuator having first and second ends attached to the load beam at firstand second attachment locations, respectively, a portion of thepiezoelectric actuator between the first and second ends remainingunattached to the load beam, so that a force out of a plane of the loadbeam is applied to the load beam in an actuated state.
 2. The disk drivesuspension assembly of claim 1 wherein the load beam includes acompliant region located between the first and second attachmentlocations so that the piezoelectric actuator supports a portion of agram load in an unactuated state.
 3. The disk drive suspension assemblyof claim 2 wherein the compliant region is located between the springregion and the head mounting region.
 4. The disk drive suspensionassembly of claim 2 wherein the compliant region is located between theactuator arm mounting region and the spring region.
 5. The disk drivesuspension assembly of claim 1 wherein the load beam includes acompliant region located between the first and second attachmentlocations so that the piezoelectric actuator bends the load beam at thecompliant region in an actuated state.
 6. The disk drive suspensionassembly of claim 1 wherein the first end of the piezoelectric actuatoris attached adjacent to the actuator arm mounting region and the secondend is attached adjacent to the spring region.
 7. The disk drivesuspension assembly of claim 1 wherein the piezoelectric actuatorexhibits a curling motion when a voltage is applied.
 8. The disk drivesuspension assembly of claim 1 wherein the piezoelectric actuator isattached to the load beam with one of a conductive adhesive and anon-conductive adhesive.
 9. The disk drive suspension assembly of claim1 wherein a gram load is changed by applying a voltage to thepiezoelectric actuator.
 10. The disk drive suspension assembly of claim1 wherein the force applied to the load beam alters a gram load with aresolution of about 0.01 grams or less.
 11. The disk drive suspensionassembly of claim 1 wherein the force is normal to the load beam. 12.The disk drive suspension assembly of claim 1 comprising a secondpiezoelectric actuator attached to the load beam at third and fourthattachment locations so that a force non-parallel to the load beam isapplied to the load beam in an actuated state.
 13. A disk drivesuspension assembly, comprising: a load beam having a distal end, anactuator arm mounting region on a proximal end, a rigid region, and aspring region between the rigid region and actuator arm mounting region;a compliant region in the load beam; a head mounting region on a distalend of the load beam for receiving a transducer head; and at least onemulti-layered piezoelectric actuator having at least two layers attachedto each other along a common surface and poled such that when energizedone layer contracts while the other expands, the piezoelectric actuatorhaving first and second ends attached to the load beam at first andsecond attachment locations on opposite sides of the compliant region,respectively, a portion of the piezoelectric actuator between the firstand second ends remaining unattached to the load beam, so that thepiezoelectric actuator supports a portion of a gram load in anunactuated state and generates a force out of a plane of the load beamin an actuated state.
 14. The disk drive suspension assembly of claim 13wherein the compliant region is located between the spring region andthe head mounting region.
 15. The disk drive suspension assembly ofclaim 13 wherein the compliant region is located between the actuatorarm mounting region and the spring region.
 16. The disk drive suspensionassembly of claim 13 wherein the piezoelectric actuator generates aforce non-parallel to the load beam in an actuated state.
 17. The diskdrive suspension assembly of claim 13 comprising a second piezoelectricactuator attached to the load beam at third and fourth attachmentlocations, the third and fourth attachment locations being coplanar withthe first and second attachment locations.
 18. A disk drive comprising:a rigid magnetic disk, a load beam having a distal end, an actuator armmounting region on a proximal end, a rigid region, and a spring regionbetween the rigid region and actuator arm mounting region; a compliantregion in the load beam; a positioning arm attached to the actuator armmounting region; a head mounting region on a distal end of the load beamincluding at least one transducer head positioned opposite the rigidmagnetic disk; and a multi-layered piezoelectric actuator having atleast two layers attached to each other along a common surface and poledsuch that when energized one layer contracts while the other expands,the piezoelectric actuator having first and second ends attached to theload beam at first and second attachment locations on opposite sides ofthe compliant region, respectively, a portion of the piezoelectricactuator between the first and second ends remaining unattached to theload beam, so that the piezoelectric actuator supports a portion of agram load in an unactuated state and generates a force out of a plane ofthe load beam in an actuated state.